Page 237 - Introduction to Petroleum Engineering

224 UPSTREAM FACILITIES
11.8 URBAN OPERATIONS: THE BARNETT SHALE

The combination of hydraulic fracturing, horizontal drilling, and a reasonable gas
price catalyzed the growth of the shale gas production industry. In 2002, Mitchell
Energy implemented horizontal drilling in the Barnett Shale in North Texas. The
Barnett Shale in the United States is up to 450 ft thick and covers an area of over
2
5000 mi . A vertical well, which may pass through 400 ft of shale, can extract gas
from a much smaller volume than a horizontal well that could run through two miles
or more of shale. Figure 11.13 shows that a horizontal well can intersect more of
the reservoir when the areal extent of the reservoir is substantially larger than the
thickness of the reservoir. The orientation of man‐made fractures associated with
hydraulic fracturing depends in part on the orientation of the well and also on the
rock properties of the reservoir.
Hydraulic fracturing had been used for years, but the results had limited success.
Horizontal drilling made it possible for horizontal wellbores to contact a much
larger volume of the reservoir than vertical drilling. The combination of hydraulic
fracturing and horizontal drilling increased the rate that gas could be produced
from targets like gas‐rich, low‐permeability shale. Multiple wells drilled from a
single well pad decrease the need for large numbers of potentially noisy and aes-
thetically unappealing surface well sites. With multiwell drilling sites, the number
of locations that must have pipelines for transporting fluids and that must be oper-
ated and maintained is minimized, saving time and money for operators. Horizontal
drilling makes it possible to locate a well site outside of a highly populated area
and drill underneath the population without being seen or heard. This development
has further increased interest in shale gas because a large volume of shale gas is
found under large cities. A small operational footprint increases public support for
urban drilling.

Vertical Horizontal
well well

Overburden

Barnett shale

Fractures

Viola
Ellenburger (water bearing)
FIgURE 11.13 Schematic of Barnett Shale cross section.